An automatic chest compressor is used to repeatedly compress and release the chest of a patient to aid in breathing while other measures are taken. Such chest compressor is usually applied by an emergency worker who leaves an ambulance while carrying considerable life saving equipment (e.g. oxygen tank and regulator, defibrillator, bandages, medicines and needles, etc.) that may be useful to the patient whom he is initially approaching. In order to encourage emergency workers to carry a chest compressor, the chest compressor must be of moderate volume, especially small thickness, as well as of low weight. In order for a chest compressor to be effective, it must compress the chest sufficiently (e.g. at least one or two inches) and with sufficient force (a plurality of 10's of pounds), to obtain useful compressions of the patient's chest.
Previous chest compressors have included a metal piston that is repeatedly moved down by high pressure fluid such as pressured air applied above the piston. Such devices have an initial height considerably greater than the piston stroke length, and a considerable weight. An automatic chest compressor that could provide forceful long stoke chest compressions, but that had a small weight and volume, especially a small thickness, would be of value.